In present-day society, computer systems have been indispensable for providing the active basis supporting our life. Such a computer system as above is required to continue service for 24 hours without stopping. Available as one of these computer systems is an on-line system employed in banks and the like which handles database business affairs as a key or core process. The database business affairs are updated frequently and are therefore permitted of no complete or thorough stoppage. But, on the other hand, there is a demand for creating backups in expectation of protection of data to be handled.
In the database, data to be handled are stored in volumes (hereinafter abbreviated as VOL's) representing memory areas or storages areas precedently set in a disk device so constructed as to include a storage medium such as a magnetic disk and the data are processed. The VOL is a unit of the memory area and is sometimes called by the name of partition. The VOL is identified with a physical VOL identifier (PVID) and the computer system recognizes the VOL by acquiring VOL information through the use of the PVID. The PVID and VOL information are acquired by a disk management program and saved in a disk management information buffer on an operating system (OS). It will be appreciated that a variety of PVID's are available and in an OS called AIX (registered trademark of IBM Inc.), for instance, the PVID is handled in the form of hexadecimal data such as “005247772d2f36b”. An application such as database and the OS accesses (reads and writes) a VOL recognized on the basis of information in the buffer. Let us consider an instance where, for example, an application program accesses a file. In this case, on the basis of a physical device name corresponding to the file to be accessed (hereinafter also termed a physical name and as an example of concreted data, “hdisk0” is used in, for example, the OS called AIX (registered trademark of IBM Inc.), identification information (physical address such as LUN) in a disk device of a physical memory medium identified (from the OS) by that physical device name is designated and a request for access to the disk device is transmitted. At that time, verification is carried out as to whether a PVID stored in a given area of the memory medium to be accessed coincides with a PVID stored in the aforementioned disk management information buffer. If the result of verification shows non-coincidence between the PVID's, this result is handled as an access error.
As will be seen from the above, a technique of realizing a replication of VOL without causing the database to stop thoroughly is important. The prevention of complete stoppage intends to attain recovery of a system within a short period of time in the range of not causing troubles in business affairs even in the event that the system becomes faulty so that system users may be prevented from recognizing that the system stands stopped. To this end, a technique disclosed in U.S. Pat. No. 6,401,178 (corresponding to JP-A-2002-41368) is known according to which replica of data in a disk is executed in a disk device and this technique is applied to VOL's to provide a technique called VOL replica. The VOL replica includes two means for pair construction and pair division directed to paired VOL's of original VOL representing a data replication source and copy VOL representing a data replication target. The pair construction is means for fast creating a copy VOL representing a replica of an original VOL by making coincident (synchronized) all data pieces including PVID's of original/copy VOL's and VOL information. Accordingly, in a status of pair construction, the PVID's of the original/copy VOL's are coincident with each other, thereby providing a function of enabling the host computer system to recognize the original/copy VOL's impersonating a sole VOL. On the other hand, the pair division is means for cancelling the synchronization of the original/copy VOL's and rewriting the PVID of the copy VOL of the paired VOL's taking the pair construction into a PVID different from that of the original VOL. This provides a function of dividing the paired VOL's recognized as a sole VOL by the host computer system during pair construction and enabling the system to recognize the original and copy VOL's as different VOL's. These two means provide a function of creating a replica of the original VOL at a high speed and permitting the computer system to operate a replicated copy VOL.
On the other hand, a computer system required to have high reliability of recovery within short period of time is so constructed as to include an active computer or a active computer for executing processes and a standby computer for taking over a process in the event that a fault occurs in the active computer. A cluster program for managing the active and standby computers provides a procedure for handing the process to the standby computer at the time that the fault occurring in the active computer is detected. For handing over the process, data used in the application and OS must be handed over. For example, in the aforementioned database system, it becomes necessary that information concerning a VOL in which data to be handled is stored be handed over.